1. Technical Field
Embodiments of the subject matter disclosed herein generally relate to methods and systems and, more particularly, to mechanisms and techniques for measuring a fluid flow in a pipe.
2. Discussion of the Background
During the past years, with the increase in price of fossil fuels, the interest in developing new production fields has dramatically increased. However, the availability of land-based production fields is limited. Thus, the industry has now extended drilling to offshore locations, which appear to hold a vast amount of fossil fuel. One characteristic of the offshore locations is the high pressure to which the drilling equipment is subjected. For example, it is conventional to have parts of the drilling equipment designed to withstand pressures between 5,000 and 30,000 psi. In addition, the materials used for the various components of the drilling equipment are desired to be corrosion resistant and to resist high temperatures.
Existing technologies for extracting oil from offshore fields use a system 10 as shown in FIG. 1. More specifically, the system 10 includes a vessel (or rig) 12 having a reel 14 that supplies power/communication cables 16 to a controller 18. The controller 18 is disposed undersea, close to or on the seabed 20. In this respect, it is noted that the elements shown in FIG. 1 are not drawn to scale and no dimensions should be inferred from FIG. 1.
FIG. 1 also shows that a drill string 24 is provided inside a riser 40, that extends from vessel 12 to a BOP 28. A wellhead 22 of the subsea well is connected to a casing 44, which is configured to accommodate the drill string 24 that enters the subsea well. At the end of the drill string 24 there is a drill bit (not shown). Various mechanisms, also not shown, are employed to rotate the drill string 24, and implicitly the drill bit, to extend the subsea well. The dirt and debris produced by the drill string 24 are removed by circulating a special fluid, called “mud”, through an inside of the drill string 24 and then through an annulus formed between the outside of the drill string 24 and an inside of the riser 40. Thus, the mud is pumped from the vessel 12 through the drill string 24 down to the drill bit and back through the annulus of the riser 40 back to the vessel 12.
However, during normal drilling operation, unexpected events may occur that could damage the well and/or the equipment used for drilling. One such event is the uncontrolled flow of gas, oil or other well fluids from an underground formation into the well. Such event is sometimes referred to as a “kick” or a “blowout” and may occur when formation pressure inside the well exceeds the pressure applied to it by the column of drilling fluid (mud). This event is unforeseeable and, if no measures are taken to prevent it, the well and/or the associated equipment may be damaged. Although the above discussion was directed to subsea oil exploration, the same is true for ground oil exploration.
Thus, a blowout preventer (BOP) might be installed on top of the well to seal the well in case that one of the above events is threatening the integrity of the well. The BOP is conventionally implemented as a valve to prevent the release of pressure either in the annular space, i.e., between the casing and the drill pipe, or in the open hole (i.e., hole with no drill pipe) during drilling or completion operations. Recently, a plurality of BOPs were installed on top of the well for various reasons. FIG. 1 shows two BOPs 26 or 28 that are controlled by the controller 18.
However, deep water exploration presents a host of other drilling problems, such as substantial lost circulation zones, well control incidents, shallow-water flows, etc. Thus, many of these wells are lost due to significant mechanical drilling problems. A common characteristic of these problems is the abnormal flow of the mud. For example, the flow rate at the surface pump may become larger than the flow rate of the return mud at the ship. This suggests that the integrity of the well is compromised and the mud is escaping into the environment. Another possibility which is more dangerous for the safety of the personnel working on the rig is when the flow rate of the returning mud is larger than the flow rate of the surface pump. This event suggests that the integrity of the well may be compromised, and/or a high pressure intrusion into the well has taken place. This high pressure gas or fluid then may make its way up the riser and blowout the rig. If these events take place, it is noted that the operator of the BOP does not have the time to react and close the BOP. These events not only may lead to loss of lives but also increase the cost of drilling and reduce the chances that oil would be extracted from those wells, which is undesirable.
Accordingly, it would be desirable to provide systems and methods that avoid the afore-described problems and drawbacks.